1. Field of the Invention
The present invention relates to a flat cable and a connection device and connection method for the same, more particularly relates to a dependable flat cable which is easy to be connected and is free from poor contact even when a tensile force acts in the longitudinal direction of the flat cable and to a connection device and connection method for the same.
2. Description of the Related Art
A flat cable 10 such as a flexible printed circuit (FPC) or flexible flat cable (FFC), as shown in FIG. 1, is constructed with a plurality of parallel strip-like conductors 1 sandwiched between insulating covering layers 2 comprised of insulating film, from two sides. At the connection termination 12 of the flat cable 10, the two insulating covering layers 2 are removed to expose the terminations of the conductors 1. The exposed terminations of the conductors 1 are connected, for example, to the core conductors of other cables etc.
When a flat cable is used in a location where it is repeatedly bent or when it is used for connection to a moving part, the insulating covering layers 2 and the conductors 1 are strongly bonded by an adhesive so as to enable them to withstand the repetitive bending load. If the insulating covering layers 2 of the flat cable are strongly bonded, however, it becomes difficult to remove the insulating covering layers 2 at the connection termination when being connected to other cables or the terminations of electrical equipment. Therefore, in the past, as shown in FIG. 2, in the process for manufacturing a flat cable 10, the insulating covering layers 2 of a continuous flat cable were previously removed at regular intervals to form insulating covering layer-free portions 19 at regular intervals of the flat cable. When connecting this flat cable, the conductors 1 were cut along the line X--X at the insulating covering layer-free portion 19 closest to the portion to be connected to form a connection termination with terminations of the conductors exposed.
Production of the flat cable shown in FIG. 2 requires the removal of the insulating covering layers 2 comprised of the insulating films at predetermined intervals along the longitudinal direction of the cable. As a method for doing this, it is a workable way to provide cutaway portions in advance in the insulating films constituting the insulating covering layers in the lamination step for laminating the insulating covering layers 2 on the two sides of the parallel array of the conductors 1. Alternatively, there is the method of intermittently feeding insulating films cut to predetermined lengths and lining them up on the conductors 1 so as to provide insulating covering layer-free portions 19 with exposed conductors 1 shown in FIG. 2 at predetermined intervals on the flat cable 10.
In the flat cable having the insulating covering layer-free portions 19 shown in FIG. 2, however, since the conductors 1 are exposed at locations forming the connection terminations, the connection to other cables and equipment becomes easy, but since the conductors 1 are exposed, those portions are very likely to oxidize and discolor or are easily contaminated by dust, oil, etc. depositing on the conductors, which has a detrimental effect on the electrical connection. In addition, the exposed conductors are likely to undergo stress and deform during transport or work. When pitches are out due to deformation, faulty connection arises, or insertion into card edge connectors becomes difficult.
Further, in the related art, as shown in FIG. 3, there are known the method of removing only one of the two insulating covering layers 2 of the conductors 1 at the connection termination 12, the method of removing the insulating films constituting the insulating covering layers to expose the termination portions of the conductors and adhere a separate reinforcing film on one side of the same by an adhesive, etc. With this type of cable, the conductors are connected by contact on only one side, so the reliability of the electrical contact is inferior to that of two-sided contact. Further, the termination processing is doubly troublesome and leads up to raising costs.
Considering the ease of connection, the present inventors proposed a flat cable 10 as shown in FIG. 4, where an interlayer film (peeling layer) 3 is partially sandwiched between the insulating films 2 and the conductors 1 at predetermined intervals in the longitudinal direction of the flat cable 10a without application of an adhesive so as to intermittently form portions where the conductors 1 and the insulating covering layers 2 are not adhered.
To form a connection termination of the flat cable 10a, a cut is required at the position of the peeling films 3 along the line X--X, the insulating covering layers 2 at the cut end are peeled away together with the peeling layers 3, and thus the conductors 1 are presumably exposed for connection.
To connect the connection termination of the flat cable 10a constituted in this manner, for example, as shown in FIG. 5, the method has been devised as connecting the exposed terminations of the conductors 1 and the core conductors 7 of the cables 6 by a connection terminal 8, forming a connector body 9 by insert molding, or more commonly called injection molding, and burying the connection portion in the connector body 9.
In such a connection structure, however, when the connection portion is covered with the molded connector body 9, the connection portion of the conductors is protected against bending, but there is nothing resisting the linear tension in the longitudinal direction of the flat cable, so there is raised a problem that the connection is likely to undergo stress and the contact of the conductor connection portion easily becomes slackened off.
The present invention was made in consideration of this situation and has as its object the provision of a dependable flat cable which is easily connected and is free from poor contact even when a tensile force acts in the longitudinal direction of the flat cable and to a connection device and connection method for the same.